There is no cure for the 3 million Americans affected by Type 1 diabetes (T1D). Even though daily insulin treatments prolong life expectancy, T1D diminishes the quality of life and leads to life threatening complications. T1D is caused by self-reactive T cell mediated death of insulin producing beta cells. In order to cure T1D, we must remove or control the self-reactive T cells. Until recently, identifying self-reactive T cells has been very difficult. However, recent advances in peptide-MHC tetramer technology and enrichment approaches have allowed us to identify, track and interrogate individual CD4+ T cell clones in both mouse models and humans with T1D. We have generated and validated 2 HLA DQ8 and 3 HLA DR4 diabetes relevant tetramer reagents. The goals of this proposal are to utilize these novel peptide:MHC II tetramer reagents to track and phenotype CD4+ T cell clones involved in human T1D pathogenesis. Currently there are two limitations preventing the successful use of these T1D biomarkers in the clinic. The first problem is that multiple T cell clones cannot be simultaneously analyzed due to limited reagent color combinations. This analysis must be done sequentially for each T cell tetramer. This is further complicated by the fact that individual CD4+ self-reactive clones are exceedingly rare in PBMC samples and must be correctly identified using a double staining protocol using the specific T cell tetramer in two distinct colors. Secondly, we are limited by sample volumes due to the fact that many new onset and patients at risk for developing T1D are children. In this proposal we propose to overcome these two limitations though two distinct but complementary multiplexing assays using CyTOF and flow cytometry. Results from these studies could lead to novel methods for a comprehensive analysis for earlier diabetes diagnosis in humans and novel biomarkers to monitor immune function and therapeutic efficacy in the clinical setting. The rationale for the proposed research is that with a better assay to identify and track multiple self-reactive T cell populations during T1D we will be able to develop translational approaches to selectively eliminate self-destructive T cells to cure autoimmune diabetes.